This invention concerns low-pressure metal casting in a recessed sand mold comprising a casting chamber opening downwardly, at least one impression, and ingates connecting the casting chamber to the or impression(s). The base of the casting chamber is connected to the upper end of a feed tube supplying molten metal, and the metal is made to rise in the tube until it fills the impression(s) via the ingates.
A low-pressure casting method (see, for example, commonly assigned French Patent Nos. 2,295,808; 2,367,566; and 2,556,996) is particularly advantageous, when compared with gravitational casting, for the production of thin-walled metal parts and/or parts having complex shapes and/or parts of large size. In fact, the pressure exerted by the metal, which results from the injection of a gas inside a water-tight cavity containing the molten metal, may be closely and accurately controlled to push the metal into all of the innermost recesses of the impressions.
However, using some casting mold configurations, certain casting defects linked to the filling operation, e.g., small pressurized gas pockets (i.e., incorporation of air bubbles) are seen to appear.